Reproductive function in female rats submitted to chronic hypobaric hypoxia.

Female rats were submitted to 5,500 m simulated altitude (50.7 kPa) for 23 weeks in a hypobaric chamber. In vitro biosynthesis of estradiol from labelled pregnenolone was studied in the ovaries of these rats and of their controls at sea level barometric pressure. The weight of the ovaries expressed as mg/rat was 63% higher (p < 0.001) and estradiol biosynthetic capacity expressed as % conversion/rat was 140% higher (p < 0.01) in hypoxic than in control rats. Estrous cycle and fertility were studied in rats submitted to 4,400 m simulated altitude (58.6 kPa) and in their controls. The percentage of estrous was significantly higher in hypoxic than in control animals. The fertility was lower in hypoxic rats. Optical microscopy showed signs of polycystic ovaries in both hypoxic groups. These results may suggest that the normal reproductive function includes oxygen dependent factors.

Changes in the renin-angiotensin-aldosterone system in rats of both sexes submitted to chronic hypobaric hypoxia.

The effect of moderate chronic hypobaric hypoxia (CHH) on the renin-angiotensin-aldosterone system has been analysed in male and female intact and castrated rats. The experimental animals were submitted to a simulated altitude of 4,400 m during ten weeks. Half of the experimental and half of the control animals were castrated at three weeks of age. Arterial pressure (AP) was measured once a week during the whole experimental period. Blood samples were obtained by decapitation at the end of the study. Red cell volume, plasma renin activity (PRA), plasma angiotensinogen (Ao) and aldosterone concentration (ALDO) were determined in the blood samples. Results have shown that the female animals subjected to CHH had lower levels of AP than the control female rats during all the studied periods whereas the AP of male hypoxic rats was only transiently diminished. All these changes were abolished by castration. PRA was not altered in either sex. The enzymatic complex was higher in male than in female control animals and decreased after castration in both hypoxic and control male rats. Ao was decreased by CHH in both sexes of intact rats and in female castrated animals. The renin substrate was higher in male than in female intact rats and decreased after castration in male animals. ALDO was increased after CHH only in male rats. Control female rats have higher levels of ALDO than male animals. Changes in the renin-angiotensin-aldosterone system related to CHH and also significant differences between sexes suggest that adrenal and gonadal corticosteroids may be involved in the main alterations presently observed.

The renin-angiotensin-aldosterone system in rats of both sexes subjected to chronic hypobaric hypoxia.

Plasma renin activity (PRA), plasmatic aldosterone, haematocrit, haemoglobin concentration and plasma proteins were measured in 36 Wistar rats of both sexes submitted to 380 mmHg in hypopressure chamber during 7 months and in a group of control animals (15 male and 15 female rats). PRA was significantly increased in hypoxic male (P less than 0.05) and female (P less than 0.01) rats. On the contrary, plasma aldosterone concentration did not show any significant variation. There thus was a clear dissociation between the plasmatic renin-angiotensin system and the aldosterone in rats of both sexes submitted to severe chronic hypobaric hypoxia.

Steroid biosynthesis by gonads of rats submitted to chronic hypobaric hypoxia.

In vitro biosynthesis of steroids by testes and ovaries was studied in rats submitted to 6,000 m simulated altitude for 23 weeks and their controls at sea level atmospheric pressure. Gonads' homogenates were incubated in the presence of 4(-14) C-pregnenolone and cofactors. Extractions, partitions, paper chromatography and finally crystallizations until constant specific activity were performed. Tritium labelled internal standards were used to correct for methodological losses. In male animals, only androstenedione biosynthesis calculated per rat as well as the weight of the testes were reduced in hypoxia. Nevertheless, this reduction was accompanied by an equivalent decrease in body weight; testosterone biosynthesis was not significantly changed. On the contrary, in females, estradiol biosynthesis and the weight of the ovaries were significantly higher in hypoxic than in control animals. Macroscopic and microscopic aspect of the ovaries in hypoxic rats also indicate a hyperactivity of the steroidogenic function. Weight curves and mortality studies confirmed previous findings about the advantage of females in adaptation to hypoxia. Results show that ovaries play an active role in this process.

Steroid biosynthesis by gonads of rats submitted to chronic hypobaric hypoxia

In vitro biosynthesis of steroids by testes and ovaries was studied in rats submitted to 6,000 m simulated altitude for 23 weeks and their controls at sea level atmospheric pressure. Gonads’ homogenates were incubated in the presence of 4(-14) C-pregnenolone and cofactors. Extractions, partitions, paper chromatography and finally crystallizations until constant specific activity were performed. Tritium labelled internal standards were used to correct for methodological losses. In male animals, only androstenedione biosynthesis calculated per rat as well as the weight of the testes were reduced in hypoxia. Nevertheless, this reduction was accompanied by an equivalent decrease in body weight; testosterone biosynthesis was not significantly changed. On the contrary, in females, estradiol biosynthesis and the weight of the ovaries were significantly higher in hypoxic than in control animals. Macroscopic and microscopic aspect of the ovaries in hypoxic rats also indicate a hyperactivity of the steroidogenic function. Weight curves and mortality studies confirmed previous findings about the advantage of females in adaptation to hypoxia. Results show that ovaries play an active role in this process.

Steroid biosynthesis by gonads of rats submitted to chronic hypobaric hypoxia.

In vitro biosynthesis of steroids by testes and ovaries was studied in rats submitted to 6,000 m simulated altitude for 23 weeks and their controls at sea level atmospheric pressure. Gonads homogenates were incubated in the presence of 4(-14) C-pregnenolone and cofactors. Extractions, partitions, paper chromatography and finally crystallizations until constant specific activity were performed. Tritium labelled internal standards were used to correct for methodological losses. In male animals, only androstenedione biosynthesis calculated per rat as well as the weight of the testes were reduced in hypoxia. Nevertheless, this reduction was accompanied by an equivalent decrease in body weight; testosterone biosynthesis was not significantly changed. On the contrary, in females, estradiol biosynthesis and the weight of the ovaries were significantly higher in hypoxic than in control animals. Macroscopic and microscopic aspect of the ovaries in hypoxic rats also indicate a hyperactivity of the steroidogenic function. Weight curves and mortality studies confirmed previous findings about the advantage of females in adaptation to hypoxia. Results show that ovaries play an active role in this process.